Ammonia-adding system for ammonia-based desulfurization device

ABSTRACT

Ammonia-adding apparatus and methods for ammonia-based desulfurization use multi-stage control, calculate a theoretical amount based on gas amounts provided by an inlet continuous emission monitoring system (CEMS) and an outlet CEMS of the ammonia-based desulfurization device or associated gas amounts, a SO 2  concentration provided by the inlet CEMS, and a predetermined SO 2  concentration of the outlet CEMS. The apparatus and methods calculate a corrected theoretical amount of ammonia using half of the ratio of the actual amount of added ammonia to the actual amount of removed sulfur dioxide as a correction coefficient for the theoretical amount of ammonia, add an ammonia absorbent equivalent to the corrected theoretical amount of ammonia to the ammonia-based desulfurization device through an ammonia metering means and an ammonia control valve, and automatically control the actual ammonia flow rate based on the actual SO 2  concentration and a change trend provided by the outlet CEMS.

This application is a continuation of U.S. application Ser. No.16/158,481, filed on Oct. 12, 2018, which claims the benefit of U.S.application Ser. No. 15/953,703, filed on Apr. 16, 2018, now U.S. Pat.No. 10,159,929, issued Dec. 25, 2018, which claims the benefit of U.S.application Ser. No. 15/661,186, filed on Jul. 27, 2017, now U.S. Pat.No. 10,099,170, issued Oct. 16, 2018, which claims priority under 35U.S.C. § 119 of Chinese Patent Application No. 201710446925.2, filed onJun. 14, 2017, all of which are hereby incorporated herein in theirentireties.

TECHNICAL FIELD

The present invention belongs to the field of environmental protectiontechnologies, and in particular to an ammonia-adding system for anammonia-based desulfurization device.

BACKGROUND

At present, limestone desulfurization process and ammonia-baseddesulfurization process are mainstream processes in the whole world forremoving sulfur dioxide from gases. In the limestone desulfurizationprocess, large quantities of waste water and gypsum residues areproduced during desulfurization, and a lot of investment and operatingcosts are required to treat these waste water and waste residues. Also,in the limestone desulfurization process, while 1 ton of sulfur dioxideis removed, about 0.7 ton of carbon dioxide is produced synchronously.With ammonia-based desulfurization process, basically no waste water orwaste residue is produced, and added ammonia desulfurizer is convertedinto a useful ammonium sulfate fertilizer, thus it is moreenvironmentally friendly. However, the existing ammonia-baseddesulfurization process often has the problems, such as ammonia escape,aerosol formation, etc.

Chinese patents CN 1283346C and CN 1321723C disclose a process forremoving SO₂ from coal-fired flue gas by using ammonia as a removalagent, in which the SO₂ concentration in the clean gas is less than 100mg/Nm³. However, the amount of ammonia escaping in the clean gas can beup to 12 mg/Nm³.

Chinese Patent CN 100428979C discloses an ammonia-based desulfurizationprocess with crystallization inside a tower and an apparatus thereof,wherein the desulfurization tower is designed to be of a multi-sectionstructure, successively including an oxidation section, acrystallization section, a cooling absorption section, a main absorptionsection, and a dehydration-demisting section from bottom to top. In theprocess, the evaporating ability of flue gas is utilized forcrystallization to reduce operation energy consumption, the SO₂concentration in the clean gas is less than 200 mg/Nm³, and the ammoniacontent in the clean gas can be as low as 3 mg/Nm³.

Chinese patent application No. CN 201710154157.3 discloses a method anda device for ammonia-based removal of sulfur oxides and dust from gas,wherein the device consists of a gas purification and removal system, anoxidation system, an ammonium sulfate post-processing system, an ammoniasupply system and an auxiliary system, and uses a process of multipointammonia addition and multi-stage control, thereby significantlyinhibiting ammonia escape and aerosol formation, and achieving efficientdesulfurization and dedusting effects.

Chinese patent application No. CN 201610322999.0 discloses a pH-basedautomatically adjusting ammonia addition system, mainly including acontrol cabinet, an aqueous ammonia tank, a first aqueous ammonia pump,a second aqueous ammonia pump, a pressure transmitter, anelectromagnetic flowmeter, an electric control valve and a pHtransducer, wherein the control cabinet is respectively connected to thepressure transmitter, the electromagnetic flowmeter, the electriccontrol valve, and the pH transducer; the control cabinet is connectedto the first aqueous ammonia pump and the second aqueous ammonia pump;the inlet end of the first aqueous ammonia pump is connected to theaqueous ammonia tank and the outlet end of the first aqueous ammoniapump is respectively connected to an inlet of an ammonia additionchamber and an inlet of a circulating pump; the first aqueous ammoniapump is respectively connected to the pressure transmitter, theelectromagnetic flowmeter, the electric control valve and the pHtransducer; the inlet end of the second aqueous ammonia pump isconnected to the aqueous ammonia tank and the outlet end of the secondaqueous ammonia pump is respectively connected to the inlet of theammonia addition chamber and the inlet of the circulating pump; thesecond aqueous ammonia pump is respectively connected to the pressuretransmitter, the electromagnetic flowmeter, the electric control valveand the pH transducer; and the electric control valve is respectivelyconnected to the inlet of the ammonia addition chamber and the inlet ofthe circulating pump.

An automatic ammonia-adding system with stable and reliable systemoperation, a high automation degree and a simple process and beingapplicable to an ammonia-based desulfurization device is still requiredto achieve automatic multipoint ammonia addition and multi-stage controlin the ammonia-based desulfurization device, and inhibit ammonia escapeand aerosol formation.

It would therefore be desirable to provide improved apparatus andmethods for adding ammonia to a flue gas desulfurization system toovercome shortcomings in the prior art.

SUMMARY

An object of the disclosure is to provide an ammonia-adding system withstable and reliable system operation, a high automation degree and asimple process and being applicable to an ammonia-based desulfurizationdevice. The automatic ammonia-adding system may be used with a methodand a device for ammonia-based removal of sulfur oxides and dust fromgas disclosed in Chinese patent application No. CN 201710154157.3.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects and advantages of the invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a schematic diagram of an embodiment in accordance with theprinciples of the invention.

FIG. 2 is a control scheme of automatic ammonia addition in accordancewith the principles of the invention.

The drawings are exemplifications of the principles of the invention andare not intended to limit the invention to the particular embodimentsillustrated.

DETAILED DESCRIPTION Definitions

“Ammonia recovery” means that fraction or percentage of ammonia added toa gas cleaning process that is subsequently captured and extracted fromthe process.

“Dust” means a particulate material fine enough to waft along gaseousflows, when handled, processed, or contacted. It includes but is notlimited to aerosols, including solid aerosol particles and liquidaerosol particles, soot, charcoal, non-combusted coal, fine minerals,sand, gravel, salts, and any combination thereof.

“NO_(x)” means a chemical species containing nitrogen and oxygen.

In the event that the above definitions or a description statedelsewhere in this application is inconsistent with a meaning (explicitor implicit) that is commonly used, set forth in a dictionary, or statedin a source incorporated by reference into this application, theapplication and the claim terms in particular are understood to beconstrued according to the definition or description in thisapplication, and not according to the common definition, dictionarydefinition, or the definition that was incorporated by reference. In theevent that a claim term can only be understood if it is construed by adictionary, a definition set forth in the Kirk-Othmer Encyclopedia ofChemical Technology, 5th Edition, 2005, (John Wiley & Sons, Inc.) shallcontrol, if provided therein.

Apparatus and methods for adding ammonia to an absorption solution in aflue gas desulfurization system are provided.

The apparatus and methods may involve an automatic ammonia-adding systemfor an ammonia-based desulfurization device. The apparatus mayautomatically calculate a theoretical amount of ammonia based on gasamounts provided by an inlet Continuous Emission Monitoring System(CEMS) and an outlet CEMS of the ammonia-based desulfurization device(or associated gas amounts), a SO₂ concentration provided by the inletCEMS, and a predetermined SO₂ concentration of the outlet CEMS. Theapparatus may calculate a corrected theoretical amount of ammonia usinghalf of the ratio of the actual amount of added ammonia to the actualamount of removed sulfur dioxide as a correction coefficient for thetheoretical amount of ammonia. The apparatus may add an ammoniaabsorbent equivalent to the corrected theoretical amount of ammonia (forexample, within one or more of the ranges ±10%, ±5%, ±3%, ±2% thecorrected theoretical ammount) to the ammonia-based desulfurizationdevice through an ammonia metering means and an ammonia control valve,and then may control the actual ammonia flow rate based on the actualSO₂ concentration and and a change trend provided by the outlet CEMS asa feedback.

The gas amounts of the inlet and outlet CEMS (or associated gas amounts,such as boiler activity characteristics from a boiler with which thedesulfurization device is operated), the SO₂ concentrations of the inletand outlet CEMS, and the data of the ammonia metering may be uploaded toa distributed control system to calculate the actual amount of addedammonia and the actual amount of removed sulfur dioxide, and thencalculate the theoretical amount of ammonia, the correction coefficientfor the amount of ammonia, and the corrected theoretical amount ofammonia.

The theoretical amount of ammonia, the correction coefficient for thetheoretical amount of ammonia, and the corrected theoretical amount ofammonia may be calculated as follows:

theoretical amount of ammonia=(gas amount of the inlet CEMS orassociated gas amount (Nm³/h)*inlet SO₂ concentration (mg/Nm³)−gasamount of the outlet CEMS or associated gas amount (Nm³/h)*predeterminedSO₂ concentration of the outlet CEMS (mg/Nm³))/1000/1000/64*34 kg/h

correction coefficient for theoretical amount of ammonia=actual molarnumber of added ammonia/actual molar number of removed sulfur dioxide/2

corrected theoretical amount of ammonia=theoretical amount ofammonia*correction coefficient for theoretical amount of ammonia

The apparatus may use an outlet SO₂ concentration as a term in thecorrection coefficient for the theoretical amount of ammonia. Differentcorrection coefficients can be set according to different ranges of theSO₂ concentration, such as 20-30, 50-80, 120-170 mg/Nm³ and so on.

The apparatus may use a slope of a temporal curves of the outlet SO₂concentration value to determine the outlet SO₂ concentration changetrend. Different further correction coefficients can be used fordifferent observed slopes (for example, when the slope takes on valuessuch as less than 0, 0-1, 1-2, etc.).

The methods may include adding ammonia to the absorption solution at abase rate that is proportional to: a) a target sulfur dioxide removalrate; and b) a correction coefficient that includes a ratio ofcumulative ammonia added to cumulative sulfur dioxide removed. Themethods may include; after the adding, controlling ammonia addition to asecond rate based on a measured output sulfur dioxide characteristic.

The methods may include dispensing ammonia through a valve at 90-99% thebase rate.

The valve may be a main ammonia dispensing valve. The methods mayinclude dispensing ammonia through an auxiliary ammonia dispensing valveat a rate that is the base rate minus the rate at which ammonia isdispensed through the main ammonia dispensing valve.

The main valve may have a throughput setting. The methods may includequantifying a rate of change of sulfur dioxide at an inlet of thesystem; and determining that the rate of change is not greater than athreshold. The controlling may include, simultaneously: maintaining themain valve at the throughput setting; and adjusting the auxiliary valve.

The threshold rate of change may be 2%.

The method may include quantifying a rate of change of sulfur dioxide atan inlet of the system; and determining that the rate of change isgreater than a threshold. The controlling may include: resetting themain valve from the throughput setting to a new throughput setting; and,simultaneously: maintaining the main valve at the new throughputsetting; and adjusting the auxiliary valve.

In the adding, the target sulfur dioxide removal rate may be defined asa difference between: (a) the product of: (i) a gas flow ratecorresponding to an inlet of the system and (ii) an inlet SO2concentration; and (b) the product of: (i) a gas flow rate correspondingto an outlet of the system and (ii) a predetermined SO2 outletconcentration.

The methods may include receiving at a distributed control system(“DCS”) a steam generation rate from a boiler that produces the fluegas; and evaluating the gas flow rate corresponding to the inlet as thesteam generation rate. The evaluating may include using the steamgeneration rate, or a term proportional to the steam generation rate, asa proxy, in a targeted sulfur dioxide removal rate calculation, for thegas flow rate corresponding to the inlet.

The method may include receiving at a distributed control system (“DCS”)a steam generation rate from a boiler that produces the flue gas; andevaluating the gas flow rate corresponding to the outlet as the boilerload. The evaluating may include using the steam generation rate, or aterm proportional to the steam generation rate, as a proxy, in atargeted sulfur dioxide removal rate calculation, for the gas flow ratecorresponding to the outlet.

The methods may include receiving at a distributed control system(“DCS”) a boiler air flow rate from a boiler that produces the flue gas;and

evaluating the gas flow rate corresponding to the inlet as the boilerair flow rate. The evaluating may include using the boiler air flowrate, or a term proportional to the boiler air flow rate, as a proxy, ina targeted sulfur dioxide removal rate calculation, for the gas flowrate corresponding to the inlet.

The methods may include receiving at a distributed control system(“DCS”) a boiler air flow rate from a boiler that produces the flue gas;and

evaluating the gas flow rate corresponding to the outlet as the boilerairflow rate. The evaluating may include using the boiler air flow rate,or a term proportional to the boiler air flow rate, as a proxy, in atargeted sulfur dioxide removal rate calculation, for the gas flow ratecorresponding to the outlet.

The methods may include receiving at a distributed control system(“DCS”), from a continuous emission monitoring system, a flue gas inletflow rate corresponding to an inlet of the system; and evaluating thegas flow rate corresponding to the inlet as the flue gas inlet flowrate.

The methods may include receiving at a distributed control system(“DCS”), from a continuous emission monitoring system, a flue gas outletflow rate corresponding to the outlet of the system; and evaluating thegas flow rate corresponding to the outlet as the flue gas outlet flowrate.

The methods may include measuring the flue gas inlet flow rate. Themethods may include measuring the flue gas outlet flow rate.

In the adding, the correction coefficient may be defined as: one halfof: a ratio of actual molar number of added ammonia to actual molarnumber of removed sulfur dioxide. The actual molar numbers may betallied over a time period. The time period may be a period of days, aperiod of weeks, a period of months, a period of years, or any othersuitable period.

The adding may include regulating the base rate to be: (a) no less than90% of a product of: (i) ammonia stoichiometrically required by thetarget sulfur dioxide removal rate and (ii) the correction coefficient;and (b) no more than 110% of the product.

The adding may include regulating the base rate to be: (a) no less than95% of a product of: (i) ammonia stoichiometrically required by thetarget sulfur dioxide removal rate and (ii) the correction coefficient;and (b) no more than 105% of the product.

The adding may include regulating the base rate to be: (a) no less than98% of a product of: (i) ammonia stoichiometrically required by thetarget sulfur dioxide removal rate and (ii) the correction coefficient;and (b) no more than 102% of the product.

The target sulfur dioxide removal rate depends on a preset outlet sulfurdioxide concentration. The ammonia stoichiometrically required may be:

$\frac{\begin{matrix}{{\begin{pmatrix}{{gas}\mspace{14mu} {flow}\mspace{14mu} {rate}} \\{{corresponding}\mspace{14mu} {to}} \\{{an}\mspace{14mu} {inlet}\mspace{14mu} {of}\mspace{14mu} {the}} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{{SO}\; 2\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {the}\mspace{14mu} {inlet}},{{mg}\text{/}{Nm}^{3}}}\end{pmatrix}} -} \\{\begin{pmatrix}{{gas}\mspace{14mu} {flow}\mspace{14mu} {rate}} \\{{corresponding}\mspace{14mu} {to}} \\{{an}\mspace{14mu} {{out}{let}}\mspace{14mu} {of}\mspace{14mu} {the}} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{{preset}\mspace{14mu} {SO}\; 2\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {{out}{let}}},{{mg}\text{/}{Nm}^{3}}}\end{pmatrix}}\end{matrix}}{( {1,000\mspace{14mu} {mg}\text{/}g} )( {1000\mspace{14mu} g\text{/}{kg}} )( {64\mspace{14mu} {mg}\mspace{14mu} {{SO}_{2}/34}\mspace{14mu} {mg}\mspace{14mu} {NH}_{3}} )}.$

The methods may include receiving, at a distributed control system(“DCS”), from an inlet continuous electronic monitoring instrument, thegas flow rate corresponding to the inlet of the system.

The methods may include receiving, at a distributed control system(“DCS”), from an inlet continuous electronic monitoring instrument, theSO2 concentration at the inlet of the system.

The methods may include receiving, at a distributed control system(“DCS”), from an outlet continuous electronic monitoring instrument, thegas flow rate corresponding to the outlet of the system.

The controlling may include: receiving at a distributed control system(“DCS”) a sulfur dioxide concentration at an outlet of thedesulfurization system; and changing the correction coefficient inresponse to the sulfur dioxide concentration.

The valve may be a main ammonia dispensing valve, and the methods mayinclude dispensing ammonia through an auxiliary ammonia dispensing valveat a rate that is the base rate minus the rate at which ammonia isdispensed through the main ammonia dispensing valve. The methods mayinclude changing the rate of dispensing through the auxiliary ammoniadispensing valve in response to a predefined relationship between: (a) arate of change of sulfur dioxide emission rate at an outlet of thesystem; and (b) a fine adjustment value. The fine adjustment value maycorrespond to a throughput setting of the auxiliary valve. The fineadjustment value may correspond to a change in a throughput setting ofthe auxiliary valve.

The controlling may include changing the correction coefficient inresponse to a sulfur dioxide concentration at an outlet of thedesulfurization system.

The method may include measuring only one of: (a) the gas flow ratecorresponding to the inlet of the system; and (b) the gas flow ratecorresponding to the outlet of the system; and evaluating the other oneas the measured one. The evaluating may include using the measured rateas a proxy, in a targeted sulfur dioxide removal rate calculation, forthe rate not measured.

The methods may include receiving at a distributed control system(“DCS”) a flue gas characteristic; and correcting the other rate basedon the flow characteristic. The other rate may be the rate not measured.The flow characteristic may be a flue gas temperature. The flowcharacteristic may be a flue gas pressure. The flow characteristic maybe a flue gas water content.

The absorption liquid may include at least one ammonia or amine basedcompound, including but not limited to ammonium salts, ammonium ions(NH4⁺), ammonium sulfate, ammonium sulfite, and any combination thereof.The liquid may be water.

The apparatus and methods may include an oxidation section, anabsorption section and a fine particulate control section in theabsorption tower.

The apparatus may include an ammonia-adding system for an ammonia-baseddesulfurization device. The apparatus may use multi-stage control. Theapparatus may include a processor. The processor may calculate atheoretical amount of required ammonia based on flue gas amountsprovided by an inlet continuous emission monitoring system (“CEMS”) andan outlet CEMS of the ammonia-based desulfurization device or associatedgas amounts, an SO₂ concentration provided by the inlet CEMS, and apredetermined SO₂ concentration of the outlet CEMS. The processor maycalculate a corrected theoretical amount of ammonia using half of theratio of the actual amount of added ammonia to the actual amount ofremoved sulfur dioxide as a correction coefficient for the theoreticalamount of ammonia. The apparatus may provide addition of an ammoniaabsorbent equivalent to the corrected theoretical amount of ammonia ±10%to the ammonia-based desulfurization device through an ammonia meteringmeans and an ammonia control valve. The apparatus may automaticallycontrol the actual ammonia flow rate based on the actual SO₂concentration and a change trend. One or both of the actual SO2concentration and the change trend may be provided by the outlet CEMS asa feedback.

The apparatus may include an absorption tower, an ammonia supply system,an ammonia control valve, an ammonia metering means, a circulating pump,an inlet CEMS, an outlet CEMS and an oxidation section.

The gas amounts of the inlet and outlet CEMS or associated gas amounts,the SO₂ concentrations of the inlet and outlet CEMS, and the data of theammonia metering may be uploaded to the DCS to calculate the actualamount of added ammonia and the actual amount of removed sulfur dioxide,and then calculate the theoretical amount of ammonia, the correctioncoefficient for the amount of ammonia, and the corrected theoreticalamount of ammonia.

The theoretical amount of ammonia, the correction coefficient for thetheoretical amount of ammonia, and the corrected theoretical amount ofammonia may be calculated as follows:

Theoretical Amount of Ammonia:

theoretical amount of ammonia=(gas amount of the inlet CEMS orassociated gas amount (Nm³/h)*inlet SO₂ concentration (mg/Nm³)−gasamount of the outlet CEMS or associated gas amount (Nm³/h)*predeterminedSO₂ concentration of the outlet CEMS (mg/Nm³))/1000/1000/64*34 kg/h

Correction Coefficient for Theoretical Amount of Ammonia:

correction coefficient for theoretical amount of ammonia=ratio of actualmolar number of added ammonia to actual molar number of removed sulfurdioxide/2

Corrected Theoretical Amount of Ammonia:

corrected theoretical amount of ammonia=theoretical amount ofammonia*correction coefficient for theoretical amount of ammonia.

An outlet SO₂ concentration gradient (change in concentration per unitof time) may be a term in the correction coefficient for the theoreticalamount of ammonia.

A slope of curve of the outlet SO₂ concentration value may be evaluatedto assess an outlet SO₂ concentration change trend.

The ammonia absorbent supplied by the apparatus may be one or more ofliquid ammonia, aqueous ammonia and gas ammonia.

The apparatus may include one or more ammonia control valves. Theapparatus may include two ammonia control valves. The apparatus mayinclude a plurality of ammonia control valves having different controlabilities.

A control valve with a large control ability may be used to control thecorrected theoretical amount of ammonia. A control valve with a small,or fine, control ability may be used for automatic feedback adjustmentand control.

The apparatus may include a flow meter or a metering pump for meteringor adding ammonia.

The inlet CEMS may output one or more of water content, temperature andpressure of the flue gas.

The outlet CEMS may output one or more of water content, temperature andpressure of the flue gas.

A boiler may be associated with the desulfurization device. The boilermay receive heat from hot gas that is then exhausted as flue gas fortreatment by the desulfurization device. The apparatus may substitutefor one or both of the inlet and outlet CEM gas amounts a boiler steamgeneration rate (tons per unit of time, for example) (a “boiler load”)and a boiler air amount.

The apparatus may substitute the inlet CMS gas amount for the outlet CMSgas amount. The apparatus may substitute the outlet CMS gas amount forthe inlet CMS gas amount.

One or more of the water content, temperature and pressure data of theinlet and outlet CEMS may be used for gas-amount correction.

Some embodiments are discussed with reference to FIG. 1. In someembodiments, the apparatus may include ammonia supply system 2, ammoniacontrol valve 3, ammonia metering means 4, inlet CEMS 7 and outlet CEMS8. In some embodiments, the apparatus may include absorption tower 1,ammonia supply system 2, ammonia control valve 3, ammonia flow meter 4,circulating pump 6, inlet CEMS 7, outlet CEMS 8 and oxidation section 9.

The apparatus may provide an ammonia absorbent, which may be one or moreof liquid ammonia, aqueous ammonia and gaseous ammonia.

The apparatus may include one or more ammonia control valves. Theapparatus may include two or more ammonia control valves. The valves mayhave different control abilities. For example, one or more of the valvesmay have large (coarse) control ability, and one or more of the valvesmay have fine control ability. A control valve with a large controlability may be used to control 90-99% amount of ammonia. A control valvewith a small control ability may be used for automatic feedbackadjustment and control.

In some embodiments, the ammonia metering means may include one or bothof a flow meter, e.g. a volumetric flow meter or a mass flow meter, anda metering pump.

In some embodiments, the measured items for the inlet CEMS may includeone or more of a gas amount (flow rate), a gas SO₂ concentration, a gaswater content, a gas dust content, a gas temperature, and a gaspressure.

In some embodiments, the measured items for the outlet CEMS may includeone or more of a gas amount, a gas SO₂ concentration, a gas watercontent, a gas dust content, a gas temperature, a gas pressure, a gasnitrogen oxide content, and a gas free ammonia content.

In some embodiments, associated gas amounts, e.g. gas amounts calculatedfrom a boiler load, a boil air volume or other parameters may be used tosubstitute for one or both of a CEMS gas inlet amount and a CEMS gasoutlet amount. In some embodiments, one of a CEMS gas inlet amount and aCEMS gas outlet amount can be substituted for the other. In someembodiments, one or more of a gas water content, a gas temperature and agas pressures of the inlet or outlet CEMS can be used for gas amountcorrection calculation.

In some embodiments, an ammonia-based desulfurization device usingapparatus and methods may include one or more of the followingillustrative process steps:

A raw flue gas enters from the middle-lower part of an absorption tower.

An ammonia supply system provides supplemental ammonia absorbent via anammonia control valve to predetermined ammonia-adding points, such as anoxidation section of an absorption tower, a circulating pump, etc.,thereby achieving automatic ammonia addition to the desulfurizationsystem.

The circulating washing liquid (ammonia absorbent) may be concentrated(crystallized) in a cooling-and-washing process, and then processed toan ammonium sulfate product through an ammonium sulfate post-processingsystem.

The raw flue gas is emitted from a flue gas outlet on the top of thetower after cooling-and-washing, washing for desulfurization, andremoving fine particulate matters by a washing liquid circulated by acirculating pump.

A specific illustrative embodiment of the apparatus and methods is nowdescribed with reference to FIG. 1 and FIG. 2, wherein the automaticammonia-adding system includes an absorption tower 1, ammonia supplysystem 2, ammonia control valve 3, ammonia metering means 4, circulatingpump 6, inlet CEMS 7, outlet CEMS 8 and oxidation section 9.

A Distributed Control System (DCS) automatically calculates atheoretical amount of ammonia using a microprocessor based on gasamounts provided by inlet CEMS 7 and outlet CEMS 8 (or associated gasamounts), an SO₂ concentration provided by the inlet CEMS 7 and apredetermined SO₂ concentration of outlet CEMS 8; calculates a correctedtheoretical amount of ammonia using half of the ratio of the actualamount of added ammonia to the actual amount of removed sulfur dioxideas a correction coefficient for the theoretical amount of ammonia; addsan ammonia absorbent equivalent to the corrected theoretical amount ofammonia (for example, within one or more of the ranges ±10%, ±5%, ±3%,±2% the corrected theoretical ammount), to the ammonia-baseddesulfurization device through ammonia metering means 4 and ammoniacontrol valve 3; and then automatically controls the actual ammonia flowrate based on the actual SO₂ concentration and change trend provided bythe outlet CEMS 8 as a feedback, thereby achieving automatic ammoniaaddition.

Different correction coefficients can be set according to differentranges of the SO₂ concentration (such as 20-30, 50-80, 120-170 mg/Nm³,and so on).

A slope of a curve of the outlet SO₂ value may be used as a basis forcalculation, and different correction coefficients can be set atdifferent slopes (the outlet SO₂ concentration change trend, e.g. lessthan 0, 0-1, 1-2, etc.).

The ammonia absorbent supplied by the ammonia supply system 2 may be 20%aqueous ammonia.

Dual control valves may be used to control automatic ammonia addition.The inlets of ammonia control valves 3 may be connected to ammoniasupply system 2. Outlets of ammonia control valves 3 may be connected toammonia addition points, such as oxidization section 9 and thecirculation pump 6. The amount of ammonia added through the main ammoniacontrol valve may be, for example, 98% of the corrected theoreticalamount of ammonia.

The measured items for inlet CEMS 7 may include one or more of a gasamount, a gas SO₂ concentration, a gas water content, a gas dustcontent, a gas temperature and gas pressure.

The measured items for outlet CEMS 8 may include one or more of a gasamount, a gas SO₂ concentration, a gas water content, a gas dustcontent, a gas temperature, a gas pressure, a gas nitrogen oxidecontent, and a gas free ammonia content.

Ammonia supply system 2 may include one or more of an aqueous ammoniatank, an aqueous ammonia unloading pump, an aqueous ammonia supply pump,an accident spray device and a breathing gas washing tank. An aqueousammonia having a concentration of 20 wt.-% may be supplied as an ammoniaabsorbent. The ammonia metering means may include a mass flow meter.

An illustrative ammonia-based desulfurization process using theapparatus and methods may include one or more of the following steps:

-   -   Raw flue gas 5 enters from the middle-lower part of the        absorption tower 1.    -   Ammonia supply system 2 provides supplemental aqueous ammonia        absorbent, via main ammonia control valve 31 and an auxiliary        ammonia control valve 32, to ammonia addition points, such as        oxidization section 9 and circulation pump 6.

A circulating washing liquid may be oxidized, then concentrated to asolid content of 10-20 wt.-% in a cooling-and-washing process, and thenprocessed to an ammonium sulfate product through an ammonium sulfatepost-processing system.

Gas 5 then may be emitted from a flue gas outlet on the top of the towersuccessively after cooling-and-washing, washing for desulfurization, andremoving fine particulate matters by a washing liquid circulated bycirculation pump 6.

In the ammonia-based desulfurization process, illustrative ammoniaaddition control steps are as follows:

-   1) uploading the gas amounts of inlet CEMS 7 and outlet CEMS 8 (or    associated gas amounts), the SO₂ concentrations of inlet CEMS 7 and    outlet CEMS 8, and ammonia metering data to the distributed control    system (DCS), wherein the water content, temperature and pressure    data of the inlet CEMS and the outlet CEMS can be used for the gas    amount correction calculation;-   2) predetermining the outlet SO₂ concentration by the DCS;-   3) calculating the theoretical amount of ammonia;-   4) calculating the correction coefficient for the theoretical amount    of ammonia;-   5) calculating the corrected theoretical amount of ammonia-   6) controlling the ammonia flow rate to be 98% of the corrected    theoretical amount of ammonia through mass flow meter 4 and main    ammonia control valve 31;-   7) acquiring the actual SO₂ concentration of the outlet CEMS by the    DCS;-   8) controlling auxiliary ammonia control valve 32 based on the    actual SO₂ concentration and change trend of the outlet CEMS as a    feedback to allow the outlet SO₂ concentration to tend towards the    predetermined SO₂ concentration; and-   9) acquiring the actual ammonia flow rate, and integrating the    actual ammonia flow rate over time; and acquiring the actual amount    of removed sulfur dioxide, and integrating the actual amount of    removed sulfur dioxide over time, by the DCS to conduct the next    round of control.

The apparatus and methods may improve the automation degree of anammonia-based desulfurization device through automatic ammonia addition,may have SO₂ concentration and total dust in the outlet clean flue gasthat do not exceed standards because of inlet gas amount and SO₂concentration fluctuations, and may reduce investment by making use ofmeasured quantities at the inlet and outlet CEMS, automatic statisticsand the computing function of the distributed control system.

Under the conditions that the SO₂ concentration is not more than 30000mg/Nm³ and the total dust concentration is not more than 50 mg/Nm³ inthe raw flue gas, the ammonia-based desulfurization device may achieve aSO₂ concentration in the clean flue gas of no more than 35 mg/Nm³, atotal dust (including aerosol) concentration of no more than 5 mg/Nm³,an ammonia escape of no more than 3 mg/Nm³, and an ammonia recovery ofno less than 99%.

The following embodiment is provided for the purpose of illustration,not limitation.

Embodiment 1

A raw flue gas was treated using the apparatus and methods, as shown inFIG. 1, wherein 1 is an absorption tower, 2 is an ammonia supply system,3 is an ammonia control valve, 4 is a mass flow meter as an ammoniametering means, 5 is the raw flue gas, 6 is a circulating pump, 7 is aninlet CEMS, 8 is an outlet CEMS, and 9 is an oxidation section. The gasamount of the raw flue gas is 360,000-510,000 Nm³/h, the SO₂concentration is 1,000-30,000 mg/Nm³, and the total dust concentrationis 15-30 mg/Nm³.

An ammonia absorbent supplied by ammonia supply system 2 is liquidammonia.

Dual control valves, i.e, a main ammonia control valve 31 and anauxiliary ammonia control valve 32, are used to control automaticammonia addition, wherein the inlets of the ammonia control valves 3 areconnected to the ammonia supply system 2, the outlets of the ammoniacontrol valves 3 are connected to the ammonia addition points, such asthe oxidization section 9 and the circulation pump 6, and the amount ofammonia added through the main ammonia control valve 31 is 99% of thecorrected theoretical amount of ammonia.

The measured items for the inlet CEMS 7 include gas amount, SO₂concentration, NO_(x) content, water content, dust content, temperatureand pressure.

The measured items for the outlet CEMS 8 include gas amount, SO₂concentration, water content, dust content, temperature, pressure,nitrogen oxides content and free ammonia content.

The ammonia supply system 2 includes a liquid ammonia spherical tank, anammonia unloading compressor, an ammonia supply pump and an accidentspray device, and the ammonia metering means 4 is a mass flow meter.

Raw flue gas 5 enters from the middle-lower part of absorption tower 1,and is then emitted from the flue gas outlet on the top of the towersuccessively after cooling-and-washing, washing for desulfurization, andremoving fine particulate matters by a washing liquid circulated bycirculating pump 6.

Ammonia supply system 2 provides supplemental liquid ammonia absorbentthrough main ammonia control valve 31 and auxiliary ammonia controlvalve 32 to the ammonia addition points, such as oxidization section 9and circulation pump 6.

The circulating washing liquid is oxidized, then concentrated to a solidcontent of 15 wt.-% in the cooling-and-washing process, and thenprocessed to an ammonium sulfate product through an ammonium sulfatepost-processing system.

Illustrative control steps were as follows:

1) acquiring relevant data by a DCS: an inlet gas amount of 395000Nm³/h, an inlet SO₂ concentration of 2112 mg/Nm³, an outlet gas amountof 405000 Nm³/h, an outlet SO₂ concentration of 24 mg/Nm³, an actualcumulative amount of added liquid ammonia of 1940 t, and an actualcumulative amount of removed sulfur dioxide of 3653 t;

2) predetermining the outlet SO₂ concentration of 23.9 mg/Nm³ by theDCS;

3) calculating a theoretical amount ofammonia=(395000*2112−405000*23.9)/1000/1000/64*34=438 kg/h;

4) calculating a correction coefficient for the theoretical amount ofammonia=1940/34/3653*64=0.9997;

5) calculating a corrected theoretical amount ofammonia=438*0.9997=437.85 kg/h

6) controlling the ammonia flow rate to 433.47 kg/h through mass flowmeter 4 and main ammonia control valve 31;

7) acquiring the actual SO₂ concentration of the outlet CEMS 23.9mg/Nm³;

8) controlling auxiliary ammonia control valve 32 based on the actualSO₂ concentration and change trend of the outlet CEMS 8 as a feedback tocontrol the outlet SO₂ concentration to 23.5 mg/Nm³; and

9) acquiring actual total ammonia flow rate of 438 kg/h and integratingand acquiring the actual amount of removed sulfur dioxide andintegrating, to conduct the next round of control.

When a change rate of a product of the inlet gas amount and the inletSO₂ concentration was less than or equal to 2%, the openness degree ofmain ammonia control valve 31 was left unchanged, and the actual SO₂value of outlet CEMS 8 was controlled to 20-25 mg/Nm³ through theauxiliary ammonia control valve 32. When the change rate of the productof the inlet gas amount and the inlet SO₂ concentration was more than2%, the openness degree of main ammonia control valve 31 was calculatedand adjusted according to the above steps, and the actual SO₂ value ofoutlet CEMS was controlled to 20-25 mg/Nm³ by controlling auxiliaryammonia control valve 32.

The resulting clean flue gas had the following characteristics:

SO₂: 23.6 mg/Nm³;

total dust (including aerosol): 1.9 mg/Nm³;

ammonia escape: 0.55 mg/Nm³; and

ammonia recovery: 99.4%.

The present disclosure illustrates principles of the invention and isnot intended to limit the invention to the particular embodimentsillustrated. All patents, patent applications, scientific papers, andany other referenced materials mentioned herein are incorporated byreference in their entirety. The principles of the invention encompassany possible combination of some or all of the various embodimentsmentioned herein, described herein and/or incorporated herein. Theprinciples of the invention encompass any possible combination that alsospecifically excludes any one or some of the various embodimentsmentioned herein, described herein and/or incorporated herein.

All ranges and parameters disclosed herein are understood to encompassany and all subranges subsumed therein, and every number between theendpoints. For example, a stated range of “1 to 10” should be consideredto include any and all subranges between (and inclusive of) the minimumvalue of 1 and the maximum value of 10; that is, all subranges beginningwith a minimum value of 1 or more (e.g. 1 to 6.1), and ending with amaximum value of 10 or less (e.g. 2.3 to 9.4, 3 to 8, 4 to 7), and toeach number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained within therange. All percentages, ratios and proportions herein are by weightunless otherwise specified.

Thus, apparatus and methods for adding ammonia to a desulfurizationsystem have been provided. Persons skilled in the art will appreciatethat the present invention can be practiced by other than the describedembodiments, which are presented for purposes of illustration ratherthan of limitation. The present invention is limited only by the claimsthat follow.

1. Apparatus for adding ammonia to an absorption solution in a flue-gasdesulfurization system, the apparatus comprising: an emission monitoringsystem configured to provide a measure of an output sulfur dioxidecharacteristic; valves configured to: add ammonia to the absorptionsolution at a base rate that is proportional to: a) a target sulfurdioxide removal rate defined as a difference between: 1) a product of: a gas flow rate corresponding to an inlet of the desulfurization systemand an inlet SO₂ concentration; and 2) a product of:  a gas flow ratecorresponding to an outlet of the desulfurization system and apredetermined SO₂ outlet concentration; and b) a correction coefficientthat includes a ratio of cumulative ammonia added to cumulative sulfurdioxide removed; and, then, control ammonia addition to the absorptionsolution to a second rate based on the measure of the output sulfurdioxide characteristic; and a distributed control system configured to:receive a flue gas inlet flow rate corresponding to the inlet of thedesulfurization system; and calculate an amount of required ammoniabased, at least partly, on the flue gas inlet flow rate, wherein the gasflow rate corresponding to the inlet is evaluated as the flue gas inletflow rate. 2-26. (canceled)
 27. The apparatus of claim 1 wherein thevalves include a main ammonia dispensing valve and an auxiliary ammoniadispensing valve, the auxiliary valve configured to dispense ammonia ata rate that is the base rate minus a rate at which ammonia is dispensedthrough the main valve.
 28. The apparatus of claim 27 wherein theauxiliary valve is further configured to change its rate of dispensingammonia based on the measure of the output sulfur dioxidecharacteristic.
 29. The apparatus of claim 28 wherein: the measure ofthe sulfur dioxide characteristic is a rate of change of sulfur dioxideemission rate at the outlet of the desulfurization system; and theauxiliary valve is further configured to change its rate based on apredefined relationship between: the rate of change of sulfur dioxideemission at the outlet; and a fine adjustment value.
 30. The apparatusof claim 29 wherein: the valves being configured to add ammoniaincludes: the main valve being configured to: pass ammonia; and becontrolled with coarse control; and the valves being configured tocontrol ammonia addition includes: the auxiliary valve being configuredto: pass ammonia; and be controlled with fine control.
 31. The apparatusof claim 1 wherein the correction coefficient is defined as: one halfof: a ratio of actual molar number of added ammonia to actual molarnumber of removed sulfur dioxide.
 32. The apparatus of claim 31 whereinthe valves are further configured to regulate the base rate to be: noless than 90% of a product of: ammonia stoichiometrically required bythe target sulfur dioxide removal rate; and the correction coefficient;and no more than 110% of the product.
 33. The apparatus of claim 32wherein: the target sulfur dioxide removal rate depends on apredetermined outlet sulfur dioxide concentration; and the ammoniastoichiometrically required is: $\frac{\begin{matrix}{{\begin{pmatrix}{{gas}\mspace{14mu} {amount}\mspace{14mu} {corresponding}} \\{{to}\mspace{14mu} {the}\mspace{14mu} {inlet}\mspace{14mu} {of}\mspace{14mu} {the}} \\{desulfurization} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{{SO}_{2}\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {the}\mspace{14mu} {inlet}},} \\{{mg}\text{/}{Nm}^{3}}\end{pmatrix}} -} \\{\begin{pmatrix}{{gas}\mspace{14mu} {amount}\mspace{14mu} {corresponding}} \\{{to}\mspace{14mu} {the}\mspace{14mu} {outlet}\mspace{14mu} {of}\mspace{14mu} {the}} \\{desulfurization} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{predetermined} \\{{SO}_{2}\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {the}\mspace{14mu} {{out}{let}}},{{mg}\text{/}{Nm}^{3}}}\end{pmatrix}}\end{matrix}}{( {1,000\mspace{14mu} {mg}\text{/}g} )( {1000\mspace{14mu} g\text{/}{kg}} )( {64\mspace{14mu} {mg}\mspace{14mu} {{SO}_{2}/34}\mspace{14mu} {mg}\mspace{14mu} {NH}_{3}} )}.$34. The apparatus of claim 33 wherein: the gas amount corresponding tothe inlet of the desulfurization system is received from an inletcontinuous electronic monitoring instrument; and the SO₂ concentrationat the inlet of the desulfurization system is received from an inletcontinuous electronic monitoring instrument.
 35. The apparatus of claim33 wherein the gas amount corresponding to the outlet of thedesulfurization system is received from an outlet continuous electronicmonitoring instrument.
 36. The apparatus of claim 1 wherein the flue gasinlet flow rate is received from an inlet continuous emission monitoringsystem.
 37. The apparatus of claim 1 wherein the distributed controlsystem uses a processor to calculate the amount of required ammonia, theprocessor configured to calculate the amount based on: characteristicsof flue gas, the characteristics provided by an inlet continuousemission monitoring system (“CEMS”) and an outlet CEMS of thedesulfurization system; an SO2 concentration provided by the inlet CEMS;and a predetermined SO2 concentration of the outlet CEMS.
 38. Theapparatus of claim 1 further configured to measure the flue gas inletflow rate.
 39. The apparatus of claim 1 further configured to: measureat least one of: a gas amount corresponding to the inlet of thedesulfurization system; and a gas amount corresponding to the outlet ofthe desulfurization system; and substitute the at least one measured oneof the gas amount corresponding to the inlet and the gas amountcorresponding to the outlet for the other one of the gas amountcorresponding to the inlet and the gas amount corresponding to theoutlet.
 40. The apparatus of claim 39 wherein the other one is subjectto a gas amount correction calculation based, at least partly, on a gasflow characteristic.
 41. Apparatus for adding ammonia to an absorptionsolution in a flue-gas desulfurization system, the apparatus comprising:an emission monitoring system configured to provide a measure of anoutput sulfur dioxide characteristic; valves configured to: add ammoniato the absorption solution at a base rate that is proportional to: a) atarget sulfur dioxide removal rate defined as a difference between: 1) aproduct of:  a gas flow rate corresponding to an inlet of thedesulfurization system and an inlet SO₂ concentration; and 2) a productof:  a gas flow rate corresponding to an outlet of the desulfurizationsystem and a predetermined SO₂ outlet concentration; and b) a correctioncoefficient that includes a ratio of cumulative ammonia added tocumulative sulfur dioxide removed; and, then, control ammonia additionto the absorption solution to a second rate based on the measure of theoutput sulfur dioxide characteristic; and a distributed control systemconfigured to: receive a flue gas outlet flow rate corresponding to theoutlet of the desulfurization system; and calculate an amount ofrequired ammonia based, at least partly, on the flue gas outlet flowrate, wherein the gas flow rate corresponding to the outlet is evaluatedas the flue gas outlet flow rate.
 42. The apparatus of claim 41 whereinthe valves include a main ammonia dispensing valve and an auxiliaryammonia dispensing valve, the auxiliary valve configured to dispenseammonia at a rate that is the base rate minus a rate at which ammonia isdispensed through the main valve.
 43. The apparatus of claim 42 whereinthe auxiliary valve is further configured to change its rate ofdispensing ammonia based on the measure of the output sulfur dioxidecharacteristic,
 44. The apparatus of claim 43 wherein: the measure ofthe sulfur dioxide characteristic is a rate of change of sulfur dioxideemission rate at the outlet of the desulfurization system; and theauxiliary valve is further configured to change its rate based on apredefined relationship between: the rate of change of sulfur dioxideemission at the outlet; and a fine adjustment value.
 45. The apparatusof claim 44 wherein: the valves being configured to add ammoniaincludes: the main valve being configured to: pass ammonia; and becontrolled with coarse control; and the valves being configured tocontrol ammonia addition includes: the auxiliary valve being configuredto: pass ammonia; and be controlled with fine control.
 46. The apparatusof claim 41 wherein the correction coefficient is defined as: one halfof: a ratio of actual molar number of added ammonia to actual molarnumber of removed sulfur dioxide.
 47. The apparatus of claim 46 whereinthe valves are further configured to regulate the base rate to be: noless than 90% of a product of: ammonia stoichiometrically required bythe target sulfur dioxide removal rate; and the correction coefficient;and no more than 110% of the product.
 48. The apparatus of claim 47wherein: the target sulfur dioxide removal rate depends on apredetermined outlet sulfur dioxide concentration; and the ammoniastoichiometrically required is: $\frac{\begin{matrix}{{\begin{pmatrix}{{gas}\mspace{14mu} {amount}\mspace{14mu} {corresponding}} \\{{to}\mspace{14mu} {the}\mspace{14mu} {inlet}\mspace{14mu} {of}\mspace{14mu} {the}} \\{desulfurization} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{{SO}_{2}\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {the}\mspace{14mu} {inlet}},} \\{{mg}\text{/}{Nm}^{3}}\end{pmatrix}} -} \\{\begin{pmatrix}{{gas}\mspace{14mu} {amount}\mspace{14mu} {corresponding}} \\{{to}\mspace{14mu} {the}\mspace{14mu} {outlet}\mspace{14mu} {of}\mspace{14mu} {the}} \\{desulfurization} \\{{system},{{Nm}^{3}\text{/}h}}\end{pmatrix}\begin{pmatrix}{predetermined} \\{{SO}_{2}\mspace{14mu} {concentration}} \\{{{at}\mspace{14mu} {the}\mspace{14mu} {{out}{let}}},{{mg}\text{/}{Nm}^{3}}}\end{pmatrix}}\end{matrix}}{( {1,000\mspace{14mu} {mg}\text{/}g} )( {1000\mspace{14mu} g\text{/}{kg}} )( {64\mspace{14mu} {mg}\mspace{14mu} {{SO}_{2}/34}\mspace{14mu} {mg}\mspace{14mu} {NH}_{3}} )}.$49. The apparatus of claim 48 wherein: the gas amount corresponding tothe inlet of the desulfurization system is received from an inletcontinuous electronic monitoring instrument; and the SO₂ concentrationat the inlet of the desulfurization system is received from an inletcontinuous electronic monitoring instrument.
 50. The apparatus of claim48 wherein the gas amount corresponding to the outlet of thedesulfurization system is received from an outlet continuous electronicmonitoring instrument.
 51. The apparatus of claim 41 wherein the fluegas outlet flow rate is received from an outlet continuous emissionmonitoring system.
 52. The apparatus of claim 41 wherein the distributedcontrol system uses a processor to calculate the amount of requiredammonia, the processor configured to calculate the amount based on:characteristics of flue gas, the characteristics provided by an inletcontinuous emission monitoring system (“CEMS”) and an outlet CEMS of thedesulfurization system; an SO2 concentration provided by the inlet CEMS;and a predetermined SO2 concentration of the outlet CEMS.
 53. Theapparatus of claim 41 further configured to measure the flue gas outletflow rate.
 54. The apparatus of claim 41 further configured to: measureat least one of: a gas amount corresponding to the inlet of thedesulfurization system; and a gas amount corresponding to the outlet ofthe desulfurization system; and substitute the at least one measured oneof the gas amount corresponding to the inlet and the gas amountcorresponding to the outlet for the other one of the gas amountcorresponding to the inlet and the gas amount corresponding to theoutlet.
 55. The apparatus of claim 54 wherein the other one is subjectto a gas amount correction calculation based, at least partly, on a gasflow characteristic.